A laser vibrometer or laser Doppler vibrometer is a scientific instrument that is used to make non-contact measurements of vibration of a surface. Generally, a laser beam is directed at the surface of interest, and scattered light from the surface is collected and interfered with the reference beam on a photodetector, typically a photodiode. The vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface. The output of a laser vibrometer is generally a continuous analog voltage that is directly proportional to the target velocity component along the direction of the laser beam.
One advantage of a laser vibrometer over similar measurement devices such as an accelerometer is that the laser vibrometer can be directed at targets that are difficult to access, or that may be too small or too hot to attach a physical transducer. Also, the laser vibrometer makes the vibration measurement without mass-loading the target, which is important for MEMS devices.
However, older laser vibrometers make measurements at a single point. It is often desirable to make measurements at multiple points on a target. While it is possible to scan the laser beam across the surface of the item of interest, this is a relatively slow process, and transient events that occur quicker than the time it takes to scan through a series of points cannot be measured. In response to this problem, multichannel and multipoint laser doppler vibrometers have been developed, where the target beam is split into a plurality of target beams. However, such multipoint laser doppler vibrometers are relatively expensive, as a separate detector is required for each of the plurality of target beams.
It would be desirable to provide a laser vibrometer which is of simple construction, which is self-synchronized, and which can readily measure non-repeatable or transient events.